PURPOSE: The purpose of this study is to assess the safety and effectiveness of a testosterone 1% hydroalcoholic (T-gel) as a means to provide androgen replacement in hypogonadal men following its daily administration for six months. The hypothesis to be tested is that the gel preparation is an effective a form of androgen replacement as the currently available cutaneous patch. Methods: Previous studies have shown cutaneous patches to be a superior delivery system compared to intramuscular injections of testosterone. In this study, patients will be monitored for testosterone changes and other hormonal levels including gonadotropins, estradiol, dyhydrotestosterone, prolactin, as well as lipid profiles, blood chemistry and blood count. In addition, prostate evaluation will be performed by rectal examination and prostate specific antigen levels. Patients will have bone formation and resorption markers measured, and bone density studies will be performed. In addition, questionnaires will be filled out by the patients regarding mood and sexual function. Patients eligible for the study will be males between the ages of 18 and 68 years of age who have been diagnosed with testosterone deficiency requiring testosterone replacement. Selected patients should be in good health without a significant systemic illness and should have no pre-existing prostate abnormalities. Most patients will be on androgen replacement and will have a wash-out period prior to protocol entry of at least six weeks for intramuscular testosterone injections and four weeks for transdermal or oral androgens. Patients will undergo a screening examination to validate their androgen deficiency syndrome and to confirm they meet criteria for protocol. Patients will be randomized to one of two doses of gel preparation, receiving either 50 or 100 mg T-gel or to a third group who will take the currently available transdermal testosterone patch. The duration of drug exposure will be 180 days and patients will be monitored on day 0, day 1, day 30, day 30, day 60, day 90, day 120, day 150 and day 180. On days 0, 1, 30, 90 and 180, patients will have blood drawn and minus30, minus15, 0, and 2, 4, 8, 12 and 24 hours after application of the gel or patch Days 60, 120 and 150 will be single a.m. blood draws in the clinic. Results: Enrollment period has ended. One patient remains to complete the study. Results are not available at this time. Two patients discontinued the study early due to adverse events. One patient discontinued due to skin intolerance of the testosterone patch, and a desire to use other erectile enhancing therapies. One patient was dropped from the study because of severe hypertension, which was not thought to be related to the study drug. Significance of the study and future plans: The significance of this study is that this gel will provide an easier delivery system compared to currently available forms of androgen replacement. While these are effective, they are relatively uncomfortable for patients. The intramuscular injection of testosterone esters is the standard androgen replacement therapy but requires injections every two weeks. This is frequently associated with the pain of a deep intramuscular injection and some scarring in the buttocks where the injection is given. The current patch, Androderm, frequently causes skin irritation. Skin irritation occurs in over half of the patients trying this form of replacement and few can tolerate this problem once it develops. The new gel formulation allows a measured dose to be given which can be rubbed on the skin by the patient. The results of this study will provide the basis for future studies.